1. Field of the Invention
The present invention relates to a carriage assembly for moving and supporting a moving access type actuator in an apparatus such as an optical disk apparatus.
2. Description of the Prior Art
FIG. 1 is a front elevational sectional view of an example of conventional carriage assembly, while FIG. 2 is a side elevational sectional view of the carriage assembly shown in FIG. 1. In these figures, a carriage 2 is adapted to be moved in the radial direction of a disk 1 which is a recording medium. A pair of first rollers 3 which are inclined to converge upward are disposed under the carriage 2. These first rollers 3 are rotatably provided on a pair of guide rails 5 in the form of round bars fixed to the base 4 and extending in the radial direction of the disk 1. Voice coils 6 having a rectangular cross-section are fixed to both sides of the carriage 2. On the outer side of the voice coil 6, there are magnets 8 which are fixed to the base 4 and adapted for moving the carriage 2 in the radial direction of the disk 1 in co-operation with the voice coil 6. A pair of second rollers 9 are rotatably mounted on both lower portions of the carriage 2. The second rollers 9 are adapted to prevent the carriage 2 from moving upward, in co-operation with the guide plate 10 secured to the base 4.
An actuator base 11 is formed within the carriage 2. The base 11 carries a lens actuator 13 which drives an objective lens 12 so as to locate the same. A light beam 14 from an optical information converter (not shown) is directed to an objective lens 12 through a triangular prism 15 which is disposed immediately under the lens actuator 13.
A description will be given hereinunder of the operation of the carriage assembly. When electrical current is supplied to the voice coil 6, a thrust force acting in the radial direction of the disk 1 (direction of X-axis in FIG. 2) is generated by the interaction between the current flowing in the voice coil 6 and the magnetic lines of force generated by the magnet 8, whereby the carriage 2 moves along the guide rail 5 with the first rollers 3 rotating on the guide rails 5. When the carriage 2 has reached a predetermined position, the electrical power supply to the voice coil 6 is interrupted so that the movement of the carriage 2 in the direction of the X-axis is ceased.
Subsequently, the lens actuator 13 operates to cause a slight movement of the objective lens 12 in the direction perpendicular to the plane of the disk 1, i.e., in the direction of the Z-axis as viewed in FIG. 1, and a light beam 14 from an optical information converter (not shown) is made to impinge upon a predetermined point on the surface of the disk 1 through the triangular prism 15 and the objective lens 12, thereby forming a light spot on the disk 1 so that recording, reproduction or erasure of information is conducted on the disk 1. The first rollers 3 secured to lower portions of the carriage 2 are inclined with respect to each other and are pressed by the guide rails 5, while the second rollers 9 are pressed by the guide plates 10, so that the movement of the carriage 2 is restricted both in the Y- and Z-axis directions. Rotation of the carriage 2 also is prevented about all the axes X, Y and Z.
This known carriage asembly suffers from a problem in that the first roller 3 on the guide rail in the form of a round bar tends to slip in the tangential direction of the guide rail when the pre-load applied to the carriage 2 is changed due to various reasons such as dimensional errors of the constituents such as the first rollers 3, second rollers 9, guide rails 5 and guide plates 10, as well as mounting error of the same. This makes it difficult to reduce the size of the first roller 3 and to precisely locate the light beam 14 with respect to the disk 1.